GRADE 5 or GRADE 8...that is the question

Generally speaking in situations where suspension pieces are involved, most folks say grade 8 is the only fastener to use. So-Cal's How to Build a Hot Rod says they (So-Cal) use grade 5 because they are slightly softer and therefore stretch more which holds parts more tightly together, but still offers awesome strength characteristics, kind of makes sense.

What's mo' bettuh in your opinion?

OH!, Lets ***ume we're talking quality American fasteners here, so as not to cornfuse the sitchie-ayshun....

 

Understand what he's meaning, but don't agree, if something 'stretches' and goes beyond its design limitations (ie elastic deformation), especially a ch***is/suspension component, then I consider that failing, or 'designing to fail'.

I appreciate that there are area's of design where this is intended, especially in engine fastener design, but not in suspension parts.

Grade 8 = my 2c

Cheers,

Drewfus

 

I use grade 8 for almost everything I bolt together. Overkill? Maybe.

 

grade 8 in my opinion...

however, i have thought about this a lot as i went to buy a couple new bolts to replace other ones.. and i think the grade 5 bending before breaking is a decent point.. that being said, you would have to look over the ch***is VERY often and be very mindfull of keeping up with anything bent..

 

I only use grade 8, but I was told Red McLeod used grade 5 on all his clutch/bellhousing set-ups for the same exact reason. Seemed to think that a 8 would snap whereas a 5 would stretch...I'm personally not looking to prove that theory correct.

 

This is true to an extent. However, a Grade 5 bolt will stretch to its limits and shear before a Grade 8 bolt will snap. I stock only Grade 8 in 3/8" and above. Its about the same price as Grade 2 or 3 if you buy in bulk like I do. Every suspension bolt is Grade 8, because I know it won't stretch or deform, and then you can get the bolt back out!

I also think back to an episode of Extreme 4x4 I saw. They had a Ranger they 4-linked, and they mentioned always using Grade 8 bolts (they mention it because they where mocking up with grade 5) and once they got it on the trail, they forgot about a Grade 5 bolt holding a link on. It sheared and took several things out with it.

I only run grade 8 in suspension of any kind. And I try to avoid single shear applications if at all possible. Bolts are meant to be a clamping application 90% of the time, not a locating device. But sometimes it just needs to be done, so I step the bolt up in size.

I also have a soft spot for that gold zinc.

 

Grade 8 fine thread..........is what I prefer to use, Littleman

 

I like 8 but on a lite car the stress would be less so a 5 may work...

 

I use grade 8 on EVERYTHING.....
but that's just because the bolt bin only has grade 8 in it.

honestly, a grade 8 bolt- even as far as stretch or maleability is concerned- is gonna be superiorto a grade 5 every day of the week. Do You really think the "bend instead of break" argument is valid here? how many of us have had a grade 8 bolt break where we would have preferred it to bend?

Think about it. Look at your average ****tershield. (to use the McLeod reference.)
In the event of a clucch explosion, the idea of the ****tershield is to contain all the high r.p.m. chunks of Iron death, right?

So lets say that we have a grade 5 bolt on the ****tershield that houses a 45 pound flywheel. add the clutch and pressure plate, and You have roughly 80 pounds of **** doing it's version of a blender in there.

that grade 5 bolt, for all of it's stretchy glory, will SHEAR well before the 8 will. meaning Your ****tershield is no longer Your salvation, and is now part of the problem. the grade 8 bolt will allow for the much softer ****tershield to deform around it well before it will break.

Sure, They're not neccecary on Your water pump. it only takes about 35 pounds of torque to really hold that ****er on there. 35 pounds of torque shouldn't deform a 3/8th 16 bolt- of any grade- enough to talk about.


Suspension parts...If You're wishing something bent before it broke...That seems a bit counterproductive. seems like it would be a non issue by that point, anyway.

 

[I also have a soft spot for that gold zinc.[/quote]

and You can buff it to shiny chrome awesomeness.

all told, the gold color represents all of those race car parts I used to handle every day...I like it too.
But, I am also a muscle car guy, so it's just more proof there's no accounting for taste.

 

SoCal actually makes sence. By bending before it snaps, you may earn some time. The question is at what point do 5 or 8's snap. If the grade 5 is bending at the point where the grade 8 is snapping, grade 5 would be the better of the two.

Oh, I use grade 5 and have for quite a while when I was into other cars. No problems so far.

 

A 1/4" Grade 5 bolt has a tensile strength rating of 120 ksi.

A 1/4" Grade 8 bolt has a tensile strength rating of 150 ksi.

​

[FONT=Arial, Helvetica, sans-serif]Grade 8 bolt capability in yield (stretch) = 130,000 lbs / in2 x .03349 in2 = 4354 lbs minimum[/FONT]​

[FONT=Arial, Helvetica, sans-serif]Grade 8 bolt capability in tension (failure) = 150,000 lbs / in2 x .03349 in2 = 5024 lbs minimum[/FONT]
[FONT=Arial, Helvetica, sans-serif]Grade 5 bolt capability in yield (stretch) = 92,000 lbs / in2 x .03349 in2 = 3081 lbs minimum[/FONT]
​

[FONT=Arial, Helvetica, sans-serif] Grade 5 bolt capability in tension (failure) = 120,000 lbs / in2 x .03349 in2 = 4019 lbs minimum[/FONT]
​

[FONT=Arial, Helvetica, sans-serif][/FONT]
​

http://www.rockcrawler.com/techreports/fasteners/index.asp​

 

Regardless, I prefer Grade 8, and thats what I keep in stock. Its never failed me. And if you design your parts correctly, it will never fail you either.

 

Lest we forget, make sure you're torquing nuts and bolts to the correct ft/lbs. depending on the application.Tthat can effect any nut or bolt regardless of grade.

 

Very good point Fred.

There is a great book out that explains the use of bolts, engineering involved in them and the way they are made, properly installing and torquing them down.

Its called Engineer To Win by Carroll Smith.


Its the same thing thats in his Nuts, Bolts, Fasteners book, but its cheaper and has a lot of other priceless information for car building inside it. I'd recommend it to anyone.

http://www.amazon.com/Engineer-Motorbooks-Workshop-Carroll-Smith/dp/0879381868

 

Exactly what I was wondering about. From the book, I am to ***ume the 8 is stronger with less stretching capability and even though it shears with more force, it shears before the 5 will deform and finally shear?

 

^ The Grade 8 shear rating is higher than the Grade 5 shear rating. So a Grade 5 would be the first to shear. Its almost 1,000 lbs difference in a small 1/4" bolt.

[FONT=Arial, Helvetica, sans-serif]Using a .250-inch diameter grade 8 fastener gives you the following shear capability:[/FONT]

[FONT=Arial, Helvetica, sans-serif]Capability in shear = 91,000 lbs / in2 x .0491 in2 = 4468 lbs[/FONT]
​

[FONT=Arial, Helvetica, sans-serif]Using the same .250-inch diameter grade 5 fastener results in the following:[/FONT]​

[FONT=Arial, Helvetica, sans-serif]Capability in shear = 75,000 lbs / in2 x .0491 in2 = 3683 lbs[/FONT]
​

 

i use only grade 8, thats all i have ever used even in my race cars

 

OEM doesnt and did NOT use grade 5 fastners for suspension. With all the bean counting going on they would have saved a penny if they could have. They didnt there. that should be enough right there. Why woul you put some thing weaker in than you take out????? makes no sense to me.... USE GRADE 8

 

so with all the fake grade 8 stuff out there, and there is a lot, I'll take a legit grade 5 over a fake 8... I keep legit 8's in the bin but I do occasionally grab something at Lowe's, but not for anything important.

 

I buy Grade 8 from Imperial Supply. Got a nice bin too, and every time you buy a box it comes with a sticky label.

And a welded Grade 8 becomes weaker than a Grade 5.

But in real world street applications, neither of them are going to break.

 

Excellent thread this! So how does one identify the fake head markings on a grade 8 bolt? I'm familiar with the head markings for the various bolt grades but fake markings...geez what's next?

 

If you torque that bolt to it's specs, it will not stretch any further.

 

I generally go buy bolts at the fastener place, by the pound, as needed for the project. Last time, it was when my daily's front U-joint wore out and the bolts in the yoke broke off instead of loosening - resulting in replacing the yoke.

Given I spend about a buck or two at a time, the few cents in difference isn't worth the risk of breaking something down the road. I even used grade eights to put the trailer hitch on - then I had a guy weld it to the frame.

 

I tend to use AN bolts in lot of ch***is applications, expensive yes - but the cost of failure is more.
The rest gets grade 8, I can't afford to stock more items than that in the shop.

 

Too bad tensile and shear strength aren't the whole story, but only a small part of it.

You could get a Ph.D in fastener design....

I don't really know what everyone is building that they need to design all of these bolts to bend and break, but I do know that you'll never find a factory car with a suspension bolt in a bending load configuration, namely because bolts aren't meant to be loaded in bending.

Bolts are for shear and axial loading.

 

Okay, let's throw in a little something more: On a scale of Grade-5 to Grade-8, where does a 1038 bolt on a Harley-Davisdon come in at? And for the guys that really know this kind of stuff. What year did H-D stop using 1038 marked bolts, and go to regular graded hardware? I don't know the answer to either, but it would be kind of neat to know.

 

Harley-Davidson, not Davison, that's a town outside of Flint, Michigan... I must go now.

 

other than "piece of mind" the grade 8 bolts also make great "eze-outs" in a pinch! i usually keep a few different size allen cap bolts for that purpose.

 

Go with grade 8 and use always use a locking nut, lock washer or Loc***e.